The speed of data transmission and reception circuits which perform data transmission and reception between boards and between cases, data transmission and reception between LSIs, and data transmission and reception between a plurality of elements and circuit blocks in a chip has been increased. Then, a data transmission clock is transmitted with data, a reception clock in a phase suitable for reception of data having the same frequency as that of a transmission clock is generated from a clock received at the reception side by a PLL circuit and the like, and transmission data is received in synchronization with the reception clock.
Furthermore, using a clock phase interpolator (PI), a reception clock in phase suitable for data reception is generated from a plurality of clocks having the same frequency as that of a transmission clock output from a PLL circuit and the like and different phases.
Linearity is an important characteristic of a clock phase interpolator (PI). The linearity of a PI output clock and the operating band thereof are in a tradeoff relationship. In an actual design, in order to improve the linearity, a band limitation is intentionally imposed by adding a fixed load to a clock path, and the like.
The linearity of the PI is dependent on process, voltage, and temperature (PVT), and varies in accordance with a fabrication process, a power supply voltage, and a temperature.
In improving the linearity by a fixed load, the fixed load is added in accordance with a case where the band is narrowed due to the process, voltage, and temperature (PVT) dependency. In this case, in a case where the band which is PVT dependent is wide, the fixed load is not sufficient, and the linearity is degraded. That is, due to PVT fluctuations, the linearity is degraded. Thus, the operating band of the PI is narrowed but, as the operating band is narrowed, the clock amplitude of a PI internal node is reduced, and an operation failure occurs. Therefore, it is not sufficient to merely narrow the band, and the band is desirably set to be an appropriate band in accordance with PVT fluctuations. Japanese Laid-open Patent Publication No. 2002-123332 is a reference document.